This study investigates whether the converting U.S. property-liability insurers improve their efficiency performance before and after the conversion. The evidence shows that converting insurers experience larger gains in cost efficiency scores and total factor productivity change than mutual control insurers before the conversion when the value-added approach is used. On the other hand, converting insurers experience deterioration in cost efficiency scores and total factor productivity change relative to mutual control insurers before the conversion when the financial intermediary approach is used. The two seemly contradictory results may be complementary because the outputs and inputs of the two approaches are different. The empirical evidences of the value-added approach and the financial intermediary approach indicate converting insurers experience improvement in their efficiency relative to mutual control insurers after the conversion. The results are robust with respect to cost efficiency scores and total factor productivity change. These overallresults support the efficiency hypothesis. The regression evidence also shows that converting insurers outperform their mutual control insurers in cost efficiency after conversion using the both approaches.